The present invention relates to a toroidal continuously variable transmission in which two sets of motion transmitting traction rollers each are disposed between and in engagement with opposite toric elements rotatably supported in the transmission housing.
The toroidal continuously variable transmissions of the above kind are disclosed in U.S. Pat. No. 4,928,542 issued on May 29, 1990; U.S. Pat. No. 4,893,517 issued on Jan. 16, 1990; and the following copending U.S. applications and EP applications. They include U.S. Pat. Appln. Ser. No. 07/316,944 filed on Feb. 28, 1989, now U.S. Pat. No. 4,968,289 U.S. Pat. Appln. Ser. No. 07/450,303 filed on Dec. 14, 1989 (=EP Appln. No. 89123151.6 filed on Dec. 14, 1989); U.S. Pat. Appln. Ser. No. 07/450,326 filed on Dec. 14, 1989 (=EP Appln. No. 89123149.0 filed on Dec. 14, 1989); and U.S. Pat. Appln. Ser. No. 07/448,194 filed on Dec. 14, 1989 (=EP Appln. No. 89123150.8 filed on Dec. 14, 1989.
In these known toroidal continuously variable transmissions, two sets of toric discs are coaxial and rotatably supported in the transmission housing such that the output toric discs are disposed between the two input toric discs which are interconnected to receive an input torque. To enable such toroidal continuously varible transmission to transmit torque, engagement forces between the input and output toric discs of each set and the traction rollers are necessary, which forces are obtained by forcing the toric discs of each set toward each other and into firm engagement with the traction rollers therebetween. The engagement forces depend on, and are generated by, the torque transmitted through the transmissions. This, however, results in a large axial thrust load of the traction rollers and the support structures for the rollers.
Opposite roller support structures for the rollers of each set have been interconnected by tension sheets which take up the opposing forces applied to the traction rollers during operation of the transmission. Each of the tension sheets has a central portion between the associated roller support structures and a guide structure associated with the central portion thereof. Each of the guide structures includes a guide block, and some of the guide blocks have been fixedly secured to the transmission housing. This arrangement prevents excessive vibration from being transmitted to the transmission housing as the tension sheets balance the forces. For withstanding the axial thrust load applied to the guide blocks, at least those portions of the transmission housing to which the guide blocks are fixedly secured ought to have a sufficiently high rigidity. This, however, results in a transmission housing with increased thickness or a transmission housing with a reinforcement rib structure.
An object of the present invention is to provide a toroidal continuously variable transmission in which it is avoided that the transmission housing needs carry the load which some or each of the guide blocks are subject to.